As electronic devices are recently miniaturized and integrated, a structural space for a cooling system is becoming very limited and narrow. Accordingly, a demand for the cooling system capable of dissipating heat at high efficiency within the narrow space is increased.
As a heat dissipating device or a cooling device, a heat pipe is mainly used. A typical heat pipe includes an empty space and a wick structure. The thinner the heat pipe, the narrower the space in which a vaporized working fluid moves due to the wick structure thereof, which results in a rapid decrease in performance thereof. Therefore, there is a limit in applying the heat pipe to ultra-thin electronic devices. To overcome the above-mentioned problem, a pulsating heat pipe is proposed. As illustrated in FIG. 1, the pulsating heat pipe includes a smooth micro tube bundle without the wick structure, and an aligned slug-train unit including a liquid slug and a vapor plug in the tube pulsates and transfers heat. The pulsating heat pipe may be manufactured to be thin because it does not have the wick structure therein and has a simple structure, which is suitable for application to microelectronic devices.
As illustrated in FIG. 2, Korean Patent Publication No. 2011-0128539 discloses a flat heat disperser including a first substrate, a second substrate which is closely coupled to the first substrate, a channel formed in a closed loop of a zigzag or spiral shape on at least one surface of the surfaces on which the first substrate and the second substrate are coupled to each other, and an injection hole formed in a portion of the first substrate or the second substrate to inject a coolant into the channel.
Such a plate pulsating heat pipe allows to self-pulsate a working fluid therein due to a pressure difference of the vapor plugs existing in an evaporator and a condenser and transfers heat from the evaporator to the condenser. However, if nucleation that generates the vapor plug in the evaporator is not properly performed, the pulsating heat pipe does not properly operate, which may cause a problem in that a temperature of the evaporator suddenly rises. In particular, in a case in which the pulsating heat pipe is used at a low heat input, a temperature overshoot phenomenon in which the temperature of the evaporator is higher than a normal operation occurs, which may cause a problem in the electronic device or durability of the electronic device to be weakened.